Descrizione: Descrizione: Descrizione: EGU Summer School 2015

 

 

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    Program

·         Timetable

·         Field program (Neves area): August 24th to 27th

·         Lecture program Bruneck (Brunico): August 27th to 30th

 

    Timetable    24-30 August 2017

    • 24th afternoon (16.00): arrival at Bruneck (Brunico) train station and transfer to the Chemnitzerhütte (Rifugio Porro) for dinner and overnight
    • 25-26th : field work on the glaciated outcrops in front of the Grosser Möseler (Mesule) glacier (photo)
    • 27th morning: move to Bruneck (Brunico)
    • 27th-30st: classroom teaching in Bruneck (Brunico)
    • August 31st morning: depart

 

Field Program

The field course will be held in the Nevessee (Lago di Neves) area (South Tyrol, northeast Italy) and will address the structural analysis of deformation structures within the Tauern meta-granitoids. The structures are present on polished outcrops at the base of the south-eastern Grosser Möseler (Mesule) glacier (Fig. 1, Fig. 2) that provide spectacular exposures for structural analysis of 2D deformation geometries. The area is located at about 2600 m and is reachable by a well-marked track from the Chemnitzerhütte (Rifugio Porro), at 2419 m. We will stay at this hut, which one reaches along a broad path from the Nevessee in about 1 hr 45 mins walking time (about a 500 m climb).
From the geological point of view, the area is located just north of a thick belt of Alpine amphibolite facies mylonites (well visible on the aerial photograph of Fig. 3), which can be investigated along the path from the hut to the glacier. The study area represents a low strain domain, which largely escaped the Alpine structural overprint. It is therefore possible to analyse in detail the progressive development of discrete ductile shear zones that exploit a network of brittle precursors (joints) and pre-existing magmatic or fluid–induced compositional heterogeneities.
During the field analysis, students will gain familiarity with the following structures:

·         magmatic structures (including different acid and basic intrusives, magma mingling, etc.): Fig. 4a, Fig. 4b, Fig. 4c, Fig. 4d, Fig. 4e);

·         joints;

·         epidote veins and alteration haloes along joints and fractures (Fig. 5a, Fig. 5b, Fig. 5c);

·         single and paired discrete shear zones nucleating on planar compositional and structural heterogeneities (Fig. 6a, Fig. 6b, Fig. 6c, Fig. 6d, Fig.6e , Fig.6f, Fig.6g);

·         quartz-biotite-plagioclase-biotite-calcite veins (Fig. 7a, Fig. 7b, Fig. 7c);

·         intersecting ductile shear zones (Fig. 8a, Fig. 8b, Fig. 8c).

·         late stage quartz-chlorite-epidote vein systems (Fig. 9a, Fig. 9b, Fig. 9c).

See all the pictures !!!

Suggested reading:

·         Mancktelow, N.S. and Pennacchioni, G., 2005. The control of precursor brittle fracture and fluid–rock interaction on the development of single and paired ductile shear zones. Journal of Structural Geology 27, 645–661. PDF


·         Mancktelow, N.S. and Pennacchioni, G., 2010. Why calcite can be stronger than quartz. Journal of Geophysical Research 115, B01402, doi:10.1029/2009JB006526. PDF


·         Pennacchioni, G. and Mancktelow, N.S., 2007. Nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions. Journal of Structural Geology 29, 1757-1780. PDF


·         Mancktelow, N. S., and Pennacchioni, G., 2013. Late magmatic healed fractures in granitoids and their influence on subsequent solid-state deformation. Journal of Structural Geology 57, 81-96.


·         Pennacchioni, G., and Mancktelow, N. S., 2013. Initiation and growth of strike-slip faults within intact metagranitoid (Neves area, eastern Alps, Italy). Geological Society of America Bulletin, 125, 1468-1483.


·         Pennacchioni, G., Ceccato, A., Fioretti, A.M., Mazzoli, C., Zorzi, F. and Ferretti, P., 2016. Episyenites in meta-granitoids of the Tauern Window (Eastern Alps): unpredictable?Journal of Geodynamics, 101, 73-87.


·         Pennacchioni, G., Mancktelow, N.S., 2018. Small-scale ductile shear zones: Neither extending, nor thickening, nor narrowing.Earth-Sciences Reviews, 184, 1-12.

 


Students will be taught to analyse:

·         the time relationships between the different intrusions of the pre-Alpine protolith;

·         the control of structural and compositional heterogeneities on nucleation of shear zones;

·         the role of fluids during ductile deformation;

·         the kinematic relationships between the different structural element of the deformation network (shear zones and veins);

·         the interference between intersecting shear zones;

·         geometry and linkage of brittle faults developed during exhumation.

Lecture Program

The second part of the school will include a series of lectures The classes will cover the following topics:

1) Solid-state ductile deformations within cooling of plutons.
Teacher: Giorgio Pennacchioni (Padua University, Italy)

The lecture will describe the solid-state deformation structures developed in different plutons (e.g.: Adamello, Southern Alps, Italy; Mono Pass Intrusive Suite, Sierra Nevada, California) during their cooling. The main focus will be on deformation structures developed at  high temperatures (T ≥ 500°C) and the role of structural (joints) and compositional (e.g. dykes) heterogeneities on nucleation of shear zones. The deformation structures in  cooling plutons will be compared with those seen during the field excursion in the Tauern metagranitoids in the Neves area. These observations provide the basis of a new model for the nucleation of ductile shear zones in granitoid plutons.

2) Fluid rock interaction in faults and shear zones.
Teacher: Stephen Cox (ANU, Australia)

(a) Physical effects of fluids on strength and mechanical behaviour of faults and shear zones
(b) Coupling between deformation and permeablity in faults and shear zones.
(c) The mechanics of high fluid flux faults - The seismogenic context
(d) Practical exercise: applications of Mohr diagrams and failure mode diagrams

3) Deformation mechanisms and strain weakening in natural shear zones.
Teacher: Luca Menegon (Plymouth University, UK)

      The lecture will show examples of deformation microstructures of quartz and feldspars in natural shear zones formed at mid- to lower-crustal conditions. The observations will be discussed in terms of (i) the effect of fluid rock interaction on the activation of different deformation mechanisms, and (ii) the implications for the strength evolution of the mid- to lower crust. The following topics will be addressed:
(a) Effect of hydrous fluids on the creep strength and deformation microstructures of quartz: comparison between "wet" and "dry" quartz
(b) Fluids, replacement reactions and deformation in granitoids
(c) Grain size reduction and transition to diffusion creep deformation in (ultra)mylonites: rheological implications

4) Rock analogue and numerical modelling of shear zone structures.
Teacher: Neil Mancktelow (ETH-Zurich, Switzerland)

(a) Strain localization and the development of heterogeneous shear zones
(b) Shear zone ends and transfer zones
(c) Stress refraction in layered and anisotropic rocks
(d) Tectonic variation in pressure in deforming rocks and its importance for controlling fluid-rock interaction
(e) Flanking structures developed around planar heterogeneities in shear zones
(f) Deformation and rotation and/or stabilization of clasts in shear zones

5) Introduction to Finite Element Modelling in Geoscience .
Teacher: Dani Schimd (Oslo University, Norway )

6) Deformation of quartz-rich rocks in nature and experiments
Teacher: Michael Stipp (Martin Luther Universität Halle-Wittenberg, Halle (Saale), Germany)

Quartz is one of the most important rock-forming mineral and significantly controls the rheology of the Earth's continental crust. Experimentally calibrated piezometer and flow laws can be used to determine stress and strain rate of natural deformation if deformation mechanisms are the same in nature and experiments, and if the deformation temperature is known. Crystal plastic deformation of quartz covers a wide range of conditions. Based on natural and experimental data it will be shown that this range can be even wider than commonly expected. Topics of this lecture are:

(a) Dynamic recrystallization microstructures of quartz in nature and experiments.
(b) Experimental piezometers and flow laws.
(c) Water weakening of quartz.
(d) Conditions of the brittle-plastic transition and crystal plastic deformation in the Earth's crust and beyond.

Practical exercises
  -Identification of recrystallization microstructures
  -Stress and strain rate determination in mylonites

6)  Role of chemical processes on strain localisation
Teacher: Philippe Goncalves (Université de Bourgogne Franche-Comté)

The aim of this lecture is to discuss the role of metamorphic and metasomatic reactions on the process of strain localisation. Using various natural examples coming from the Alps, including the Neves area, we will describe the mineralogical and chemical change involved from the early shear zone nucleation stage to the mature stage. These changes, as well as the P-T conditions of the deformation, will be modeled using phase equilibria modeling (pseudosections). All these results and observations will be used to determine how chemical and mechanical processes interact during the formation of a shear zone.

7)  Crystallographic preferred orientations and CPO-derived physical properties of rocks
Teacher: Luiz F. G. Morales (ETH Zurich - Scientific Center for Optical and Electron Microscopy)

The aim of this lecture is to present information about the development of crystallographic preferred orientation (CPOs) in geological materials, with examples, in quartz and calcite. The following topics will be addressed:

(a)   Mechanisms of formation of crystallographic preferred orientation in Earth's materials

(b)  CPO examples of quartz in nature and experiments

(c)  CPO examples of calcite in nature and experiments


Practical exercises:
-Calculation and plot of CPO of quartz and elasticity-derived properties using MTEX toolbox for Matlab (laptops with Matlab 2014 or later needed)

      

 

Further Information

o    The field area is easy of access and no climbing or special Alpine experience is required. However, the field course is in a high mountain environment and adequate equipment is essential. What do you need? Download the checklist!
The work area is at 2600m a.s.l. We will be outside the whole day (with a packed lunch provided by the hut). The weather can be warm and sunny but can also be very cold, windy and, in the worst case, snowy.

o    Course language: English.

o    Course participants: priority is given to PhD students, post-Docs and young researchers specializing in structural geology. Finishing masters students in the process of starting PhD will be considered if there are places left.

o    Course max number of participants: 35 (on a first come first served basis).


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Fifth EGU Summer School